Rotate List (LeetCode) | Interview Question Explanation

RotateList.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if(!head) return head;
        int n = 1;
        auto tail = head;
        while(tail->next) n++, tail = tail->next;
        k %= n;
        if(k == 0) return head;
        
        auto new_tail = tail;
        tail->next = head;
        
        int steps_to_new_tail = n - k;
        while(steps_to_new_tail--) new_tail = new_tail->next;
        auto new_head = new_tail->next;
        new_tail->next = nullptr;
        return new_head;
    }
};